Boundary layers, Prandtl’s and others

The concept of the boundary layer is illustrated on a spectacular scale in the circulation of the oceans. While Ludwig Prandtl’s boundary layers are regions of slow flow (relative to the boundary), the peculiarities of dynamics on a rotating sphere allow for a viscous boundary layer consisting of an intense, relatively narrow jet at the western edge of the ocean. ¹ This is the explanation for major currents such as the Gulf Stream in the Atlantic Ocean and the Kuroshio in the Pacific. Each current is about 100 km wide and 1000 km long, and transports more than 30 million tons of water per second along the coast at speeds about 100 times greater than the average speed outside the jet. Such jets are important ocean features that affect Earth’s climate.